Measuring device for scanning dimensions, especially diameters

ABSTRACT

The measuring instrument comprises a retaining fixture adapted to hold an object to be measured in a center plane of the measuring instrument, defined by a guide, in such a position that a dimension of interest will extend parallel to the guide. A carriage supporting a transmitter and a receiver, respectively, at either side of the center plane for an energy beam focused on the center plane is movable along the guide. A distance measuring device provided to measure movements of the carriage along the guide comprises a rule member which is disposed in the center plane. The dimension of interest is determined based on positions of the carriage at which the energy beam, first received by the receiver, is interrupted by the object to be measured and then again received.

BACKGROUND OF THE INVENTION

A known measuring instrument of this kind (DE 42 24 253 C1) devised formeasuring cylinders of printing presses comprises a carriage which isarranged below and parallel to a bridge of a crane assembly which bridgemoves on two rails. Two guide members protrude downwardly from thebridge, and the carriage is guided on them so as to be movable invertical direction. A distance measuring means which measures thevertical movements of the carriage is arranged outside of the spacebetween the two guide members. The carriage constitutes a transversebeam on which a retaining fixture is movable parallel to the bridge, inother words horizontally. The retaining fixture supports a dual limbbracket in such a way that the latter can be swung back and forthbetween operative and inoperative positions. When in operative position,the two limbs of the bracket extend vertically downwards so that thebracket forms an inverted U which is open at the bottom. In theinoperative position, the limbs of the bracket extend horizontally andparallel to the transverse base of the bracket. Transmitter and receiverelements, respectively, of a light barrier are arranged at the ends ofthe two limbs of the bracket. The spacing between these elements isgreater than the greatest diameter to be expected of the printingcylinders which are to be measured. A printing cylinder to be measuredis placed on a support below the transverse beam of the carriage andparallel to the same so that the bracket which has been pivoteddownwards into its operative position will embrace the printing cylinderas the carriage is lowered. The distance by which the carriage islowered while the printing cylinder interrupts the light barrier istaken as the measure of the printing cylinder diameter.

Likewise known (U.S. Pat. No. 3,555,288) is an instrument for thephotoelectric classification of objects, like sections of tree trunks.In this case the objects are movable on a guide means through aU-shaped, stationary rack. The rack comprises two hollow legs extendingvertically upwardly from a horizontal transverse member, likewise beinghollow, and they each include a vertical guide bar. On each of these twoguide bars a carriage is movable up and down. One of these carriagescarries a transmitter and the other one a receiver of a horizontal lightbarrier which is interrupted by the object to be measured. A motor ishoused inside the transverse member to serve as the common drive of bothcarriages. The motor acts through a gear box on two chain drives mountedone each in the two legs of the rack and connected to a respective oneof the two carriages.

The measuring accuracies obtainable with the two instruments describedabove are limited, both because of their structure and their designatedpurpose.

SUMMARY OF THE INVENTION

It is, therefore, the object of the invention to devise a measuringinstrument for use in scanning dimensions, especially diameters, whichinstrument provides signals suitable to be evaluated with littlecomputer expenditure and yet offering precise results of themeasurements taken.

The object is met, in accordance with the invention, by a measuringinstrument to scan dimensions, and particularly diameters of objects tobe measured, comprising a guide means which defines a center place ofthe measuring instrument, a retaining fixture having means to hold anobject to be measured in the center plane in such position that adimension of interest will extend parallel to the guide means, acarriage supporting a transmitter at one side of the center place and areceiver at the other side for an energy beam which passes transverselyof the center plane and of the dimension of interest, a distancemeasuring means to measure movements of the carriage along the guidemeans, and an evaluating means to determine the dimension of interestbased on positions of the carriage at which the energy beam, firstreceived by the receiver, is interrupted by the object to be measuredand then again received, characterized in that the energy beam isfocused on the center plane, and the distance measuring means carries arule member which is disposed in the center place. Advantageous furtherdevelopments may be gathered from the subclaims.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURES

Embodiments of the invention will be described in greater detail below,with reference to diagrammatic drawings, in which:

FIG. 1 is a side elevation of a measuring instrument according to theinvention;

FIG. 2 is the front elevation seen in the direction of arrow II in FIG.1;

FIG. 3 is the vertical cross section III--III of FIG. 1;

FIG. 4 is the vertical longitudinal section IV--IV of FIG. 3;

FIG. 5 shows a modified embodiment of the measuring instrument accordingto the invention, in side elevation similar to FIG. 1;

FIG. 6 shows the embodiment of FIG. 5 in front elevation similar to FIG.2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The measuring instrument illustrated in FIGS. 1 to 4 comprises a housing10 which is U-shaped when seen from the front, as presented in FIG. 2,and has four legs 12 including an elastic foot 14 each. The housing 10comprises two hollow turrets 16 of parallelepiped configuration betweenwhich an intermediate space 18 is defined, likewise shaped like aparallelepiped. The entire housing 10 and most of the built-instructures are symmetrical with respect to a vertical center plane 20.The two turrets 16 each are open towards the intermediate space 18through a vertical slot 22.

A pair of pillars 24 are mounted in upright position, symmetrically withrespect to the center plane 20, within the central region of the housing10, and between them a rule member 26 provided with an incremental scale28 is disposed vertically. The pillars 24 guide a carriage 30 which isU-shaped like the housing, as shown in FIG. 3, and movable in verticaldirection. A transmitter 32 and a receiver 34 for laser beams aremounted on the carriage 30 at either side of the center plane 20 and soas to be aligned with the slots 22. In its lower middle region thecarriage 30 further carries a scanning head 36 which constitutes adigital distance measuring means in cooperation with the scale 28.

One side of the carriage 30 is formed with a horizontal groove 38extending in longitudinal direction and running parallel to the plane ofthe drawings of FIGS. 1 and 4. The housing 10 has a motor 40 built ontoit, preferably an electric d.c. motor, which acts through a reductiongear 42 and a crank drive 44 arranged within the housing 10 to drive aroller 46. The roller 46 engages in the horizontal groove 38 so that thecarriage 30 will effect vertical reciprocating movements when the motor40 is operating.

The housing 10 further includes a pair of horizontal apertures 48extending in longitudinal direction, parallel and symmetrical to thecenter plane 20 and serving as supports for a retaining fixture 50. Inthe embodiment shown, the retaining fixture 50 comprises two parallel,horizontal rods 52 secured to the housing 10 by a clamping device 54 soas to be exchangeable and carrying two brackets 56. The brackets 56 areadjustable along the rods 52 and adapted to be fixed in position by atoggle 58 each.

In the case of the measuring instrument illustrated in FIGS. 1 to 4, thetwo brackets 56 each carry a mandrel 60 whose tip is located in thevertical center plane 20. One of the mandrels 60 is guided so as to bemovable longitudinally in its bracket 56, it is biased towards thehousing 10 by a spring 62 and adapted to be withdrawn by a toggle 64.The other mandrel 60 is clamped to begin with to the correspondingbracket 56 in a selectable position.

The measuring instrument according to FIGS. 5 and 6 differs from the oneillustrated in FIGS. 1 to 4 only in that instead of a mandrel 60, thetwo brackets 56 each carry a plate 66 which is adjustable in height andformed with supporting prisms 68.

According to FIGS. 1 to 4, an object to be measured 70, presented hereas a cylindrical shaft, is clamped centrally between the mandrels 60.According to FIGS. 5 and 6, on the other hand, the object to be measured70, again a cylindrical shaft, is placed on two of the supporting prisms68. In both instances the object to be measured 70 is positionedsymmetrically with respect to the center plane 20 of the measuringinstrument so that a dimension to be measured 72, in the example shown adiameter to be measured in the center plane 20, i.e. vertically, lieswithin a level ranging from the lower to the upper limits of the slots22. The dimension 72 is determined by having an energy beam 76 whichexits from the transmitter 32 and passes through the slots 22 scan thecontours 74 of the object to be measured 70, visible in the sideelevations of FIGS. 1, 4, and 5. The energy beam 76 preferably is alaser beam in the red light region and it is focused in the center plane20.

When an object to be measured has been clamped between the mmandrels 60,in accordance with FIGS. 1 to 4, or positioned on two supporting prisms68, in accordance with FIGS. 5 and 6, the transmitter 32 is switched onand the motor 40 started to operate for a period of time during whichthe crank drive 44 carries out at least one full revolution. During thistime, the carriage is moved upwardly in the direction of arrow 78,starting from its lower dead center position, shown in full lines inFIGS. 3 and 4, into its upper dead center position, indicated indash-dot lines, and back into its lower dead center position. During theupward movement, the energy beam 76 emitted by the transmitter 32 in adirection perpendicular to the center plane 20 and, at first, receivedby the receiver 34 is interrupted by the object to be measured 70. Theposition of the carriage 30 at which that happens, as determined by thedistance measuring means 28, 36, corresponds to the location of thelower contour 74 of the object to be measured 70. This position ismemorized. In the further course of the upward movement of the carriage30, the energy beam 76 which the transmitter 32 continues to radiate isreceived once more by the receiver 34 as soon at it has reached theupper contour 74 of the object to be measured 70. Again, the position ofthe carriage 30 at which that happens, as determined by the distancemeasuring means 28, 36, is memorized. The dimension 72 is derived fromthe memorized values; in the example shown, this is the diameter of theobject measured 70. The measurements may be repeated during the downwardmovement of the carriage 30, and their results may be interpolated withthe results of the measurements taken during the upward stroke.

It is likewise possible to select measuring programs with which thecarriage 30 carries out a plurality of up and down movements and acorresponding greater selection of results are obtained from themeasurements and finally interpolated.

What is claimed is:
 1. A measuring instrument to scan dimensions, andparticularly diameters of objects to be measured, comprisinga guidemeans which defines a center plane of the measuring instrument, aretaining fixture having means to hold an object to be measured in thecenter plane in such position that a dimension of interest will extendparallel to the guide means, a carriage supporting a transmitter at oneside of the center plane and a receiver at the other side for an energybeam which passes transversely of the center plane and of the dimensionof interest, a distance measuring means to measure movements of thecarriage along the guide means, and an evaluating means to determine thedimension of interest based on positions of the carriage at which theenergy beam, first received by the receiver, is interrupted by theobject to be measured and then again received, characterized in that theenergy beam is focused on the center plane, and the distance measuringmeans carries a rule member which is disposed in the center plane. 2.The measuring instrument as claimed in claim 1, characterized in thatthe energy beam is a laser beam.
 3. The measuring instrument as claimedin claim 1 or 2, characterized in that the carriage is guided on a pairof pillars disposed at either side of the center plane.
 4. The measuringinstrument as claimed in claim 1 or 2, characterized in that theretaining fixture comprises a pair of rods which extend at either sideof the center plane and parallel to the same and which carry adjustablebrackets for the object to be measured.
 5. The measuring instrument asclaimed in claims 1 or 2, characterized in that the carriage is drivenby a motor via a crank drive.